陕南镇巴地区南华系—震旦系岩石地层划分与区域对比
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摘要
为了适应国际地层学的发展趋势,在1999年12月召开的断代工作组会议上,晚前寒武纪工作组与会专家一致认为,有必要对震旦系重新定义,并决定对震旦系解体,把震旦系一分为二,原上统代表重新定义的震旦系,原下统独立新建一个系,名为“南华系”。并在第三届全国地层会议(2000年5月,北京)得到确认。
研究区所在的陕南镇巴地区曾做过大量的南华系-震旦系地层工作,但始终未能将南华系的完整地层建立起来。发现并建立起本地区完整的南华系-震旦系地层,是整个华南型南华系-震旦系研究的主要内容之一,具有重要理论和现实意义。
本文通过对陕南镇巴地区南华系-震旦系的野外调研及室内综合分析,在系统总结前人研究成果的基础上,取得了以下主要成果:
(1)通过野外实测剖面的观察和分析,对南华系-震旦系地层序列及其岩性组合特征有了清晰地认识。南华系可以划分为四套岩石地层单位:下统莲沱组、古城组、大塘坡组和上统南沱组。震旦系两套岩石地层单位为:下统陡山沱组和上统灯影组。这些地层单位可与区域上的同时代岩石地层单位进行对比。
(2)通过对采自镇巴县高桥坝地区的南沱组和莲沱组样品锆石年龄测试结果分析,镇巴地区南华系南沱组的形成下限不晚于600Ma,顶界年龄约为(634±15) Ma。镇巴地区莲沱组的形成下限不晚于670Ma,底界年龄约为(785±24) Ma。
(3)通过对南华系-震旦系进行详细观察和研究,得出冰前期—莲沱组为河、湖相沉积环境;对古城组和南沱组两套含砾岩系探讨了砾石的成因为冰碛产物,得出其沉积环境为大规模冰川覆盖的沉积环境;间冰期—大塘坡组为深水还原环境;陡山沱组反映了冰川融化后深水的沉积环境;灯影组沉积环境是大面积的海水海浸形成的浅海沉积,或台海型沉积。
(4)根据镇巴地区发育的冰碛岩特点,通过地质时代的对比,发现南华纪的两次冰期和国际上的两次冰期斯图特(Sturtian)冰期和马利诺(Marinoan)冰期有很好的对应性,总结发现镇巴地区的冰期沉积的特点既有冰水相沉积也有大陆冰川相沉积。
(5)根据Rodinia超大陆的基本概况,认识到Rodinia超大陆裂解对全球气候和构造的影响,对新元古代“雪球地球”的出现有重要的地质意义。同时,我国南华系-震旦系的地层序列对Rodinia超大陆裂解做出了响应。
In order to adapt to international trends in the development of stratigraphy,the Working Group meeting on cohort study was hold in December 1999.the The experts in working Group on Late Precambrian agreed that there is a need to redefine the Zhendan system The Sinian is redefined and Nanhua is devided from Sinian in the Third National Stratum Congress(May,2000),Formation in the Third National Conference(in May 2000,Beijing) was confirmed.
The study area located in Nanhua system,Zhendan system in Zhenba region,southern Shaanxi has done so much.But we has been unable to complete formation of the Nanhua system.Discovering and establishing completely Nanhua system,Zhendan system in this region is the main contents of the study of the type of South China,and has important theoretical and practical significance.
By outdoor and indoor comprehensive analysis about Nanhua system,Zhendan system in Zhenba region and based on a systematic summary of the results of previous studies we get the following main results:
(1) Though the field observation and research,we also regard that Nanhua is composed of four rock stratigraphic units.From bottom to top:Liantuo Formation,Gucheng Formation, Datangpo Formation and Nantuo Formation.By contrasting to existed rock stratigraphic units deposited during the same period,there is great correspondence between them,which indicates our view of Nanhua is correct.
(2) By the sampl collected from Nantuo formation and Liantuo formation in the Gaoqiao dam of Zhenba County.we get the sample analysis of test results.The age of Nantuo is no later than the lower limit 600Ma of the South no later than the lower limit 600Ma,about (634±15) The age of Liantuo formation is no later than the lower limit 670Ma,about (785±24) Ma.
(3) Based on the further study,it is believed that the sedimentary environment of the Liantuo formation belongs to lacustrine-fluvial system,and Datangpo formation belongs to deep-water reducing environment,additionally,the set of coarse-grained rocks from Gucheng and Nantuo Formations were deposited in continental glacial environment,Doushantuo reflects the melting of glaciers after the deposition of deep water environment;Dengying depositional environment is a large area sea water in shallow sedimentary formation Baptist, or the Taiwan Strait-type deposition.
(4) There are lots of observation and reserch work done on the two particular formation—Gucheng Formation and Nantuo Formation,and conjecture they are sedmentary attributable to both continental glaciation and glaciofluvial.They are homologous to two international important ice age(Sturtian Ice Age and Marinoan Ice age).
(5) The deposition feature of Zhenba area is relating to the influence of the breakup of Rodinia supercontinent in Neoproterozoic in Yangtze Landmass.The clarification of Nanhua system is contributing to establishment of systemetic stratigraphic sequence of Zhenba area, South Shaanxi Province,and is contributing to reconstruction of the tectonic evolution history of northern margin of Yangtze Landmass.
研究区所在的陕南镇巴地区曾做过大量的南华系-震旦系地层工作,但始终未能将南华系的完整地层建立起来。发现并建立起本地区完整的南华系-震旦系地层,是整个华南型南华系-震旦系研究的主要内容之一,具有重要理论和现实意义。
本文通过对陕南镇巴地区南华系-震旦系的野外调研及室内综合分析,在系统总结前人研究成果的基础上,取得了以下主要成果:
(1)通过野外实测剖面的观察和分析,对南华系-震旦系地层序列及其岩性组合特征有了清晰地认识。南华系可以划分为四套岩石地层单位:下统莲沱组、古城组、大塘坡组和上统南沱组。震旦系两套岩石地层单位为:下统陡山沱组和上统灯影组。这些地层单位可与区域上的同时代岩石地层单位进行对比。
(2)通过对采自镇巴县高桥坝地区的南沱组和莲沱组样品锆石年龄测试结果分析,镇巴地区南华系南沱组的形成下限不晚于600Ma,顶界年龄约为(634±15) Ma。镇巴地区莲沱组的形成下限不晚于670Ma,底界年龄约为(785±24) Ma。
(3)通过对南华系-震旦系进行详细观察和研究,得出冰前期—莲沱组为河、湖相沉积环境;对古城组和南沱组两套含砾岩系探讨了砾石的成因为冰碛产物,得出其沉积环境为大规模冰川覆盖的沉积环境;间冰期—大塘坡组为深水还原环境;陡山沱组反映了冰川融化后深水的沉积环境;灯影组沉积环境是大面积的海水海浸形成的浅海沉积,或台海型沉积。
(4)根据镇巴地区发育的冰碛岩特点,通过地质时代的对比,发现南华纪的两次冰期和国际上的两次冰期斯图特(Sturtian)冰期和马利诺(Marinoan)冰期有很好的对应性,总结发现镇巴地区的冰期沉积的特点既有冰水相沉积也有大陆冰川相沉积。
(5)根据Rodinia超大陆的基本概况,认识到Rodinia超大陆裂解对全球气候和构造的影响,对新元古代“雪球地球”的出现有重要的地质意义。同时,我国南华系-震旦系的地层序列对Rodinia超大陆裂解做出了响应。
In order to adapt to international trends in the development of stratigraphy,the Working Group meeting on cohort study was hold in December 1999.the The experts in working Group on Late Precambrian agreed that there is a need to redefine the Zhendan system The Sinian is redefined and Nanhua is devided from Sinian in the Third National Stratum Congress(May,2000),Formation in the Third National Conference(in May 2000,Beijing) was confirmed.
The study area located in Nanhua system,Zhendan system in Zhenba region,southern Shaanxi has done so much.But we has been unable to complete formation of the Nanhua system.Discovering and establishing completely Nanhua system,Zhendan system in this region is the main contents of the study of the type of South China,and has important theoretical and practical significance.
By outdoor and indoor comprehensive analysis about Nanhua system,Zhendan system in Zhenba region and based on a systematic summary of the results of previous studies we get the following main results:
(1) Though the field observation and research,we also regard that Nanhua is composed of four rock stratigraphic units.From bottom to top:Liantuo Formation,Gucheng Formation, Datangpo Formation and Nantuo Formation.By contrasting to existed rock stratigraphic units deposited during the same period,there is great correspondence between them,which indicates our view of Nanhua is correct.
(2) By the sampl collected from Nantuo formation and Liantuo formation in the Gaoqiao dam of Zhenba County.we get the sample analysis of test results.The age of Nantuo is no later than the lower limit 600Ma of the South no later than the lower limit 600Ma,about (634±15) The age of Liantuo formation is no later than the lower limit 670Ma,about (785±24) Ma.
(3) Based on the further study,it is believed that the sedimentary environment of the Liantuo formation belongs to lacustrine-fluvial system,and Datangpo formation belongs to deep-water reducing environment,additionally,the set of coarse-grained rocks from Gucheng and Nantuo Formations were deposited in continental glacial environment,Doushantuo reflects the melting of glaciers after the deposition of deep water environment;Dengying depositional environment is a large area sea water in shallow sedimentary formation Baptist, or the Taiwan Strait-type deposition.
(4) There are lots of observation and reserch work done on the two particular formation—Gucheng Formation and Nantuo Formation,and conjecture they are sedmentary attributable to both continental glaciation and glaciofluvial.They are homologous to two international important ice age(Sturtian Ice Age and Marinoan Ice age).
(5) The deposition feature of Zhenba area is relating to the influence of the breakup of Rodinia supercontinent in Neoproterozoic in Yangtze Landmass.The clarification of Nanhua system is contributing to establishment of systemetic stratigraphic sequence of Zhenba area, South Shaanxi Province,and is contributing to reconstruction of the tectonic evolution history of northern margin of Yangtze Landmass.
引文
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[4]中国地质调查局地层古生物研究中心.中国各地质时代地层划分与对比[M].北京:地质出版社,2005,3-63.
[5]王剑.华南“南华系”研究新进展——论南华系地层划分与对比[J].地质通报,2005,25(6):491-495.
[6]张启锐,储雪蕾.扬子地区江口冰期地层的划分对比与南华系层型剖面[J].地层学杂志,2006,30(4):306-315.
[7]张启锐,储雪蕾.南华系建系问题探讨[J].地层学杂志,2007,31(3):222-228.
[8]尹崇玉,刘敦一,高林志,等.南华系底界与古城冰期的年龄:SHRIMP Ⅱ定年证据[J].科学通报,2003,48(16):1721-1725.
[9]刘树根,李智武,刘顺,等.大巴山前陆盆地-冲断带的形成演化[M].北京:地质出版社,2006,11-23.
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